Motor control system



p 1938- G. RILEY 2,130,858

MOTOR CONTROL SYSTEM 4 Sheets-Sheet 1 Filed Nov'. 15. 1934 Fig. IA.

INVENTOR 2| Lynn a. Riley.

ATTOR%Y Sept. 20, 1938; L. G. RILEY MOTOR CONTROL SYSTEM Filed NOV. 15, 1954 4 Sheets-Sheet 2 INVENTOR Lynn 6. Riley.

/ATTORN Sept. 20, 1938; L. .G. RILEY MOTOR CONTROL SYSTEM Filed Nov. 15, 1934 4 Sheets-Sheet 4 ATTdRNE 1 M MR w My 1.

Patented Sept. 20, 1938 UNITED STATES PATENT OFFICE MOTOR- CONTROL SYSTEM Vania Application November 13, 1934, Serial No. 752,802

20 Claims.

My invention relates, generally, to motor control systems and more particularly to systems for automatically controlling the acceleration and the deceleration of the propelling motors of electric vehicles, such as street cars, subway and rapid transit trains.

An object of the invention, generally stated, is to provide an automatic control system which shall be simple and efficient in operation and which may be economically manufactured and installed. a

A more specific object of the invention is to provide for the rapid and smooth acceleration of an electrically propelled vehicle.

Another object of the invention is to maintain a uniform rate oi. acceleration of a vehicle for various loadings up to a predetermined maximum load.

A further object of the invention is to provide for smoothly decelerating a vehicle by means of electrical braking.

A still further object of the invention is to provide for decelerating an electric vehicle by electrical braking independently of the source of power for the propelling motors oi' the vehicle.

Other objects of the invention will be explained fully hereinafter or will be apparent to those skilled in the art. 1

According to one embodiment of the invention the propelling motors oi an electric vehicle are arranged for series-parallel acceleration, with bridging transition, and also for dynamic braking with the armature of one motor energizing the field winding 01' the other motor. The major portion of the accelerating resistance and part of the braking resistance is cut out of the motor circuit in small increments by means of a motordriven accelerator.

The accelerator comprises a circular copper bus divided into three insulated sections inside of which are disposed a plurality of contact fingers which are progressively forced against the bus by the action of three revolving rollers spaced 120 apart and driven by a pilot motor through a common shaft. As each contact member is pressed against the bus bar a small step of resistance-is shunted from the motor circuit. A large number 'of cam switches are located in the accelerator which function to partially control the operation of the accelerator and the propellingmotorsoi the vehicle. Additional switch '3 units are also provided for controlling the propelling motors both during acceleration and deceleration of the car. The accelerator rotation is coordinated with the operating sequence oi the switch units to produce starting, series acceleration, series-parallel transition, parallel acceleration, coasting and dynamic braking, in regular order.

For a further understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

Figures 1A, 1B, 1C and 1D constitute a diagrammatic view of a control system embodying the invention,

Fig. 2 is a schematic diagram showing the main circuit connections for the motors and control apparatus, and

Fig. 3 is a chart, showing the sequence 01' operation of a portion of the apparatus illustrated in Figs. 1 and 2.

The four sheets of the drawings may be assembled by placing Fig; 1B at the bottom of Fig. 1A, Fig. 10 to the right of Fig. 1A and Fig. ID at the bottom of Fig. 1C and to the right of Fig. 1B.

Referring to the drawings, two motors I and 2 may be utilized for propelling an electric vehicle (not shown). The motors l and 2 are of the series type, having armature windings AI and A2, and series field windings FI and F2, respectively. An electrically-operated line switch LS is provided for connecting the motors to a current collecting device 3 which engages a power conductor I. a

In accordance with the usual practice in railway control systems, the motors I and 2 are first connected in series-circuit relation and then in parallel circuit relation during the acceleration of the vehicle. Electrically operated switches J and JR are provided for establishing the series connections and switches P and G established the parallel connections.

The motors may also be connected for dynamic braking with the field winding F2 connected across the armature Al and the field winding Fl connected across the armature A2, thereby permitting the current in the armature windings to reverse and cause the motors to act as generators and retard the vehicle. A switch 13, together with the switches P and G, establishes the dynamic braking connections.

A master controller M0 is provided for controlling the motor connections both during acceleration and braking. As shown, the controller is of the drum typ having a central control "01! position with accelerating positions on one side and braking positions on the other. On the accelerating side there are three positions, namely, Switching, "Series" and Parallel. With the controller handle at the switching position, the motors are connected in series with all of the external resistance. With the handle at the series position, the control progresses automatically to the full series running position and when the handle is placed at the parallel position, the control progresses automatically to the full parallel running position, which includes shunting of the motor fields by switches SI and S4 to provide maximum speed of the motors. The automatic progression may be held at any position by returning the handle to the switching notch.

n the braking side there are a"I-Iold position and a Brake position. With the handle at the holding position the braking connections are established with all the external resistance in the circuit. When the handle is moved to the braklog position, the control automatically progresses giving the full braking effect. If at any time the handle is returned to the holding position,

the automatic progression is held until the handle is again returned to the braking position. This feature is useful in holding a train at a constant speed down a grade.

A plurality of resistors and 6 are connected in the motor circuit to control the motor current during acceleration and resistors l, 8 and 9 are also utilized during dynamic braking to contol the motor current. Resistor shunting switches El, E3, Bi, B3 and B5 are provided for shunting the resistors 5, E, l, 8 and 9, respectively. In order to simplify the mappings, the number of resistors shown been reduced, it being under stood that additional resistors and shunting switches may be readily provided.

in addition to the foregoing resistors shunting switches, a major portion of the accel= crating resistance and a part oi the braking esistance are out out of the motor in small increments b means of a motor-driven and. it, in... of contact forced against revolving unison by a common shaft i8, driven by 2. motor is which is geared to the shaft is through a shaft Elli.

The accelerator is provided with two duplic sections of resistors and each section being divided into a number of subdivisions or steps which are connected to the contact fingers ET. The resistor is connected to contact fingers (it to ti, inclusive, as shown Fig. 1C. The resistor sectionit is connected to two para el. sets of coutactfingers, the fingers ti, 3%, and 325 being connected to fingers it, 45, J6 and ll, respectively, and a roller passing over either set of contact fingers cuts out the same set of resistors. Accordingly, the roller i is prevented from engaging the contact fingers by means of a cam 2t and a push rod 363 through approximately of travel, thereby reducing &

rc e action of the the load on the pilot motor IS. The roller I3 is permitted to engage contact fingers only during dynamic braking of the motors I and 2, as will be explained more fully hereinafter.

It will be seen that contact fingers 35 and 36 will be depressed by a push rod 25, which is actuated by a cam 26, as the roller H passes over these fingers. The push rod 25 will hold the fingers 35 and 36 against the bus bar l4 after roller II has passed overthem in order that the motor circuit will not be interrupted during transition from series to parallel operation.

As shown in Fig. ID, a number of cam switches A, D, E, H, K, L, M, N, V, W, Y and T are located in the accelerator I0 and actuated by the shaft i8, which also drivesthe rollers ll, [2 and IS. The reference numerals 3| to 48, inclusive, indicate the contact fingers over which the roller i l travels while the cam switches are closed. The function of the various cam switches will be explained as the description of the control system proceeds.

The pilot motor i9 is provided with two field windings 21. and 28, one for each direction of rotation. A brake 29 is provided for stopping the motor, the brake release coil being connected in series with the pilot motor and deenergized when the motor is deenergized. The pilot motor is at all times under the control of a relay PR and is energized directly from the source of control potential, which may be a battery or other reliable source of power, independently of the master controller.

The speed or the pilot motor i 5 during acceleration is controlled by accelerating relays AIM and ARE? and also by a current liniit relay LA, the coil of which is energized by the traction motor current. The operating coils of the relays ARI and A122 are energized through retardation contr er 5 I which is inertia pendulum device sponcls to acceleration deceleration ml is provided with contact members Te closed. at prede for t. it

(not shown eleratiou; to ma n,

ucrs F is w -elay .JA sl c. third resistor to to a e speed. of c-h, in turn, decreases the across the armature or the pilot motor.

At no during the starting cycle does the accelerator stop movi g, unless the master controller moved bacir to the switching position. wever, during" the traction motor is held constant at all speeds and all car w a limit relay LB being connected to govern the progressive closing all B and 1 .3" switches during braking and also to stop ncl start the pilot motor, as the generated current may permit.

-5 the master controller handle is returned to the off position during acceleration while the I8 to be stopped.

traction motors are connected in series, the accelerator returns to the initial position. The cam switch H in the circuit of the field winding 28 of the pilot motor I8 limits the back-H feature to accelerator positions below full series. From all other positions, the cam switch K carries the rotation forward. In the event that the master controller is moved to a braking position while the traction motors are connected in series, a relay AR3 maintains the forward operation of the pilot motor until the cam switch K is closed, thereby permitting the accelerator to advance to the braking positions.

At any time during acceleration or braking the progress of the accelerator may be stopped by moving the master controller handle to the switching or the hold position. During acceleration, moving the controller to the switching position causesthe resistors and 8 to be inserted in the traction motor circuit and the pilot motor I! .the controller handle is moved to the hold position during braking, the shunting oi the braking resistors is discontinued and the braking rate is gradually reduced.

In order that the functioning of the ioregolng apparatus may be better understood, the operation of the control system will now be described. Assuming that it is desired to start the vehicle and accelerate to the maximum speed, the master controller MC may be moved to the full parallel position, thereby closing the line switch LS to connect the motors I and 2 to the power source. The energizing circuit for the actuating coil of the line switch LS may be traced from a positive conductor 8I through contact members 82 and 83, bridged by a contact segment 84, conductor 85, the coil of the switch LS, conductor 88 and the cam switch A on the accelerator III to a negative conductor 81. A holding circuit is established for the coil of the line switch, when it closes, through an interlock 88 on the line switch.

Followingthe closing of the line switch LS, the switches J and JR are closed to connect the motors I and 2 in series circuit relation. The energizing circuit for the actuating coil of the switch J may be traced from a contact finger I0, which engages the contact' segment 64 on the master controller MC, through conductor 88, an interlock II on the switch LS, conductor I2, an interlock I3 on the switch (3, conductor 14 and the actuating coil of the switch J to a negative conductor I8. The circuit through the actuating coil of the switch JR extends from the previously energized conductor 14 through the coil of the switch JR, conductor 18' and the cam switch D to the negative conductor 81.

The traction motors I and 2 are now connected in series circuit relation and In series with all the external resistance in the motor circuit, thereby causing the train to move slowly. The motor circuit maybe traced from the power conductor 4 through the current collector 3, conductor H, the contact members LSI, conductor 18, resistor; I, conductor II, the armature A-l, conductor 8I,-neld winding PI, conductor 82, the resistor 23 in the accelerator I 8, conductors 83 and 84, the contact finger 3|, which is depressed against the bus bar. I4 by the roller .I I, the bus bar II, conductor 88, the contact members JRI, conductor 88, the resistor 23 in the accelerator I8, conductors 81 and 88, the field winding F2,

conductor 88, the armature A2, conductor II,.

the coil of the limitrelay LA. conductor 82, the resistor 8, and conductor 88 to ground at 84.

The main contact members RIA and R3A oi the resistor shunting switches RI and R3, respectively, are next closed by interlock progression to shunt the resistors 5 and 6 from the motor circuit. The circuit for the actuating coil oi the switch RI may be traced from a contact finger 95 on the master controller MC through conductor 86, an interlock 81 on the line switch LS, conductors 88 and 98, an interlock IOI on the switch JR, conductors I02 and I03, an interlock III! on the switch RI, conductor I05 and the actuating coil of the switch RI to a negative conductor I08. As soon as the switch RI closes, a circuit is established for the switch R3 which extends from the previously energized conductor I03 through an interlock I01 on the Switch RI. conductor I08, an interlock I09 on the swiich R3, conductor III and the actuating coil of the switch R3 to a negative conductor II2.

Following the closing of the switch R3, the PR relay is energized, thereby establishing an energizing circuit for the pilot motor I9 which drives the rollers in the accelerator I0, thereby shunting the resistance in the accelerator from the traction motor circuit and causing the speed 01 the traction motors to increase. gizing circuit for the actuating coil of the PR relay may be traced from the previously energized conductor I08 ihrough an interlock H3 on the switch R3, conductors II! and H5, an interlock II8 on the switch JR, conductors II! and H8 and the actuating coil of the relay PR to a negative conductor H8. The PR relay establishes a circuit for the pilot motor I9 which extends from a positive conductor I2I through contact members I22 on the PR relay, conductor I23, a resistor I24, the field winding 21 and arma ure of the pilot motor I8, conductor I25, and the release coil of the brake 29 to a negative conductor I26.

The accelerator I0 continues to cut resistance out of the motor circuit under the control of the retardation controller 5| and the accelerating relays ARI and AR2, as explained hereinbefore, until the roller II depresses finger 35. At this point, the push rod 25 is actuated by the cam 28, as previously explained. to depress fingers 35 and 38 against the bus bar I4. When the roller II is on finger 38, the cam switch D is opened, thereby interrupting the circuit through the actuating coil of the switch JR which permits the switch to open. The traction motors I and 2 are now in the series running position, the motor The enercircuit extending from the bus bar II through controller through conductor I28, an interlock III on the switch JR, conductor I32, an interlock. I33 on the line switch LB, conductor I34, the

cam switch W, conductor I83, the interlock I01 on the switch RI, conductor I88, the interlock II3 on the switch R3, conductor II, the cam switch M, conductor I38, an interlock I38 on the switch 3 and conductors I31 and III to the actuating coil oi the relay PR. v

As explained hereinbei'ore, the purpose of the push rod 25 and the locking cam 25, which retains the fingers 35 and 36 in contact with the bus her H after the roller i I has passed over these fingers, is to prevent opening the main motor chcult during the transition period.

When the roller H is on contact finger 31' of the accelerator, the cam switch V closes, thereby causing the switches P and G to close. The energizing circuit for the actuating coil of the switch- 6: may be traced from the previously energized conductor l3? through the interlock M3 on the switch LS, conductors I38 and its, the actuating coil of the switch G, conductor M! and the cam switch V to the negative conductor 61. The circuit for the actuating coil of the switch 1? extends from the conductor B39 through conductor 2, the coil of the switch P, and thence through conductor Hi to the negative conductor 6?.

The closing of the switch G causes the switch. J to open, since the circuit through the interlock E3 is interrupted, and the transition is now complete, the traction motors l and 2 being connected in parallel-circuit relation, and each motor in series with one-half of the resistors mounted 5 on the accelerator ill. The circuit through the motor may he traced from the line switch Hill through conductor [8, the contacts INA, conductor l8, armature At conductor 8% field winniins, conductor the resistor conductors 83 and 5, the contacts conductor 93 to ground at The circuit through the motor 2; may "be traced from the contacts LS5 of the line switch tl'ircugh' conductor M3, the contacts i, conductors [M and esistor 22, conductor El 88, the ii no conductor it, le armature the coil. of the the contacts i.

ilers continues he roller depresses 2e roller [2 depresses shunting the re on; the moi-or t the cam switch T over the conmg the resistors 55, i with. the armature descri bed. conductors 42 the pilot motor se coil. of the c. the accelerais closed, of the field g the field y be shunted (it, respectively, by rs SlA'ancl 54A enticing the energizing 5'6 switch Si may conductor he line switch 1 conouctor conductor i536, e conta ct doctors E54 and switch S5, conductor l v e actuating coil of the switch S5 negative conductor [58. Upon the clo g? of the switch S[, the actuating coil of the S4 is energized through a, cir

wt a

- when.

arouses cult which extends from the previously energized conductor Hi5 through an interlock E59, conis attained by shunting the motor fields and the motors will continue to operate at balancing speed until the master controller handle is returned to the on" position to permit coasting of the car, in

which event the line switch LS is opened to disconnect the traction motors from the power source. The opening of the line switch establishes an energizing circuit for the pilot motor H! which will cause the accelerator roller H to be advanced to the contact finger 43 while the vehicle is coasting. This circuit may be traced from a positive conductor 565 through an interlccl: Hi6 on the line switch LS, conductor Hi1, an interlocl-r. M8 on the PR. relay, which was deenergizeci when the master controller was moved to the off position, conductors 69 and ill, the cam sWitchQli'Z, conductor E23, the resistor [24, field winding ill, the armature of the motor 19, conciuctor and the release coii of the brake 29 to the negative conductor H6. The sccelerator will come to rest with he roller it on connger since the cam switch K is opened the finger is reache Fro? the co g operation power Ina? 1e eapplieo to the traction motors or cynam may he applied, depending, of course, up ex:- te al conditions. In case it is desired to reapply parser to the tsction motors, the master controilei' handle of the running 2o one otion motor time, since H depn cositions. Hon ver,

not he esta coil oi tuating scrib o the line con tact finger E l motor en ltcl- 1 he tracer earn 5 the switch B, con. of the PR 1' 'cy to e conductor H9. From this point, not ,1 vcl to the traction motors i and Z in same manner as hezreinbefore described.

In, case it is desired to apply dynamic braking to the motor, the roaster controller handle is moved from coa 1g is ull braking position, thereby closing t 1e switches P, G and B to establish the dynamic bra-icing connections. The circuit for the actuating coils of the switches P and l gel [12 on the anci 29, thence oughtne the switches P and. G and cam switch V to a negative conductor as previously described. The

circuit through the actuating coil of the switch B extends from the interlock I'M on the line switch LS through conductor N5, the actuating coil of the switch B, conductor I18 and the cam switch Y to the negative conductor 61.

As previously described, the field winding F2 01' the motor2 is connected across the armature AI 01 the motor I and thefield winding Fl of the motor I is connected across the armature A2 of the motor 2 during dynamic braking, which permits the motors to function as generators, thereby decelerating the car. The circuit through the armature AI andthe field winding F2 extends from one terminal of the armatureAl through conductor 18, resistor 5, conductors -18 and I43,

the contact members PI of the switch P, conductors I44 and 88, the resistor 22, conductors 81 and 88, field winding F2, conductors 89 and I11, resistor I18, the contacts BA of the switch B, resistors 1, 8 and 8, the coil of the limit relay LB, conductor I18, the coil oi limit relay AL and conductor I8I to the other terminal of the armature Al. The circuit through the armature A2 and field winding Fl extends from one terminal of the armature A2 through conductor I11, the resistor I18, the contact members BA of the switch -B, resistors 1, 8 and 8, the coil of the limit relay LB, conductor I18, the coil of the limit relay AL, conductor I8I, the field winding FI, conductor 82, a resistor 28, conductors 88 and 84, the contacts 8|, conductor 88, resistor 8, the coil of the limit relayv LA and conductor 8I to the other terminal of the armature A2.

It will be recalledthat during the acceleration period the roller I2 pertormedno electrical function, since it was held away from the contact fingers on the accelerator by means of the cam 24. When the roller II reaches finger 48, the roller I8 is released and depresses finger 81. During the final 120 for the braking section of the accelerator travel, rollers I I and I2 function as a single roller, since the contact fingers which they simultaneously depress are electrically connected together.

The auxiliary limit relay AL which is energized during ynamic braking, prevents the shunting of the motor field windings FI and F2 until a predetermined current value has been reached, thereby ensuring that full field excitation is provided for the motors I and 2, causing the generated current to build up rapidly and the braking action to take efiect quickly. However, it is undesirable to suddenly produce too great a braking eflect. Therefore, the auxiliary limit relay AL is set' to cause the motor field windings to be shunted at a comparatively low current value.

The switches BI, B2 and BI, which shunt the braking resistors 1, 8 and 8, start closing by interlock progression upon the establishment of I the dynamic braking circuit. The energizing circult for the actuating coil of the switch BI extends irom a contact finger I82 "on the master controller MC through conductor ill, the cam switch L, conductor I84, the contact member ll! of the limit relay LB, conductor I82, an interlock I81 on the switch B, conductor I88, an interlock I88 on the switch BI, conductor I8I and the actuating coil of the switch BI to a negative conductor I82. 1

When the switch BI closes, the circuit is established for the actuating coil of the switch D2 which extends from the previously, energized conductor I88 through an interlock I88 on the switch BI, conductor I84, an interlock I88 on the switch B8, conductor I88 and the actuating coil of the switch B8 to the conductor I81.

Likewise. upon the closing of the switch B8 a circuit is established for the actuating coil of switch B5, which extends from the previously energized conductor I94 through an interlock I88 on the switch B3, conductor I88, an interlock 28I on the switch B5, conductor 282 and 5 the actuating coil of the switch B5 to a negative conductor 283. In this manner the switches BI, B3 and B5 are closed by interlock progression to shunt the resistors 1, 8 and 9, respectively, from the motor circuit, the rate of closing ofthe 10 switches being controlled by the braking limit relay LB in a manner well known in the art.

At some point in the closing sequence of the switches Bl, B3 and B5, the generated current reaches a value sufficient to close the auxiliary 5 limit relay AL, which 'permits shunting the motor fields by closing the field shunting switches SI and S4. The energizing circuit for the actuating coil of the switch SI may be traced from the previously energized conductor I84 through 20 the contact members 284 of the limit relay AL, conductors I54 and I55, an interlock I56 on the switch SI, conductor I51 and the actuating coil of the switch SI to the negative conductor I58.

The switch S4 is closed by interlock progression 25 in a manner previously described.

When the switch B5 is closed, a circuit is established for the actuating coil of the switch RI, which extends from the previously energized conductor I88 through an interlock 285 on the switch 3 B5, conductors 286 and I 83, an interlock I84 on the switch RI, conductor I85 and the actuating coil of the switch RI to the negative conductor I88. When the switch RI closes to shunt the resistor 5, the switch R8 is closed by interlock 5 progression to, shunt the resistor 8, as previously described. However, the closing of the switches RI and R8 is controlled by the braking limit relay LB in the same manner as is the closing of the switches BI, B8 and B5. 4

braking section, which is the mm or travel.

However, the progression 01' the accelerator is under the control 01' the braking limit relay LB. since the energizing circuit for the PR relay, which controls the pilot motor I8 is established by the contact members 01 the limit relay LB. The limit relay LA does not function during dynamic braking, but *controls the speed of the pilot motor only during acceleration in the manner described hereinbeiore.

88 The cam switch L opens at the end of the braking cycle, thereby stopping the pilot motor I8 with roller II on contact finger 48. It will be noted that the resistor I18 is not shunted from the motor circuit during dynamic braking. This 65 resistor permits the braking tractive eiiort to gradually fade out as the speed of the car is decreased and the air brakes may be used to bring the car to a complete stop.

It will be noted that dynamic braking oi the 7 vehicle can be maintained regardless of whether or not the current collector 2 is in contact with the power conductor 4, as the traction motors are disconnected from the power source during dynamic braking and all of the control appa- 71:

ratus, including the accelerator I0, is operated from an independent control source, such as a battery.

When the master controller handle is returned to the off position, the accelerator rollers remain in the final braking position until another acceleration is to be made and the master controller is moved to one of the accelerating positions, whereupon the accelerator returns to the starting position, the PR relay being energized through a circuit established through the cam switch N, as previously described.

As stated hereinbefore, if during the accelerating period, the master controller handle is returned to the oil! position before the accelerator roller II has reached finger 36, the accelerator returns to the initial position. The cam switch H, through which the circuit for the reverse field winding 28 of the'pilot motor I! is established, limits the back-oil feature to accelerator positions below the full series. From all-other positions the cam switch K carries the rotation of the accelerator forward. The circuit which energizes the pilot motor for reverse operation may be traced from a positive conductor 209 through an interlock III on the line switch LS.

conductor III, an interlock I on the PRrelay, conductor 2, an interlock II! on the relay ARI, conductor 2|, the cam switch H, conductor ill, the reverse field winding 28 and the armature of the pilot motor l8,-conductor I25 and the release coil of the brake 29 to the negative conductor I".

As described hereinbefore, the relay ARI is provided to permit the, accelerator to rotate in the forward direction to .the braking position instead of returning to the initial position in the event that the master controller handle is moved to a dynamic braking position while the traction motors are connected for series operation. As shown on the diagram, the contact members 2|. of the relay AR; are connected across the conductors I23 and I'll, thereby paralleling the cam switch K when therelay ARI is energized, which causes the accelerator III to be advanced to the braking position. The energizing circuit for the actuating coil of the relay AR! extends from the controller finger III on the master controller through conductor I'll, an interlock I'll on the line switch LS, conductors I88, I38 and iii, an interlock 12! on the switch P, conductor 222 and the actuating coil of the relay ABS to a negative conductor 223.

In addition to the foregoing described apparatus, anumber of protective interlocks are shown embodying the-invention herein disclosed, it is believed to be unnecessary to specifically describe them in the present specification.

Fromthe foregoing description, it is apparent that I have provided a control system which will cause the propelling motors of an electric vehicle to be accelerated rapidLv and smoothly. It is also by ensuring that both the acceleration and braking of the vehicle will be produced smoothly without discomfort to the passengers.

Since numerous changes may be made in the above described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a control system, in combination, a plurality of resistor sections, a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for moving the contact members into engagement with the bus-bar, means for actuating the rollers, and means for controlling the operation of the last-named means.

2. In a control system, in combination, a plurality of resistor sections, a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for moving the contact members into engagement with the bus-bar, a common shaft for operating all of said rollers, means for driving said shaft, and means for controlling theor'aeration of the last-named means.

3. In a control system, in'combination, a plurality of resistor sectionsr a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for pressing the contact members into engagement with the bus-bar, a common shaft for 0D- crating all of said rollers, a pilot motor for driving of the pilot motor.

5. In a control system, in combination, a plurality of resistor sections, a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar to shunt the, resistor sections, a plurality of rollers for moving the contact members into engagement with the bus-bar, means for actuating the rollers in unison, means for withholding one of said rollers from engaging said contact members during a portion of its cycle of operation. and means for controlling the operation of the roller actuating means.

6. In a motor control system, in combination, a plurality of motors, a source of power for the motors, a plurality of resistor sections for con- 7. In a motor control system, in combination. a plurality of motors, a source oi power for the motors, a pluralityof resistor sections for controlling the motor current, a circular bus-bar divided into a plurality of sections, a plurality oi. contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for moving the contact members into engagement with the bus-bar, means for actuating all of said rollers in unison, and means responsive to the motor current for'controlling the operation of the lastnamed means.

8. In a motor control system, in combination, a plurality of motors, a source of power for the motors, a plurality of resistor sections for controlling the motor current, a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for pressing the contact members into engagement with the bus-bar, a common shaft for operating all of said rollers in unison, a pilot motor for driving said shaft, and means responsive to the motor current for controlling the speed of the pilot motor.

9. In a motor control system, in combination, a plurality of motors, a source of power for the motors, switching means for connecting the motors to the source of power, a plurality oi! resistor sections for controlling the motor current, a circular bus-bar divided into a plurality of sections, a plurality 01' contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for pressing the contact members into engagement with the bus-bar, means for actuatingthe rollers, and means dependent upon the position ot said rollers for controlling the operation of said switching means.

10. In a. motor control system, in combination, a plurality of motors, a source of power for the motors, switching means for connecting the motors to the source of power, a plurality of resistor sections for controlling the motor current, a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for moving the contact members into engagement with the bus-bar, means for actuating the rollers, interlock means actuated by said switching means, and means dependent upon the position of said rollers and cooperating with said interlock means for controlling the direction oif rotation of the rollers.

11. In a motor control system, in combination,

pilot motor for actuating the roller, and means responsive to the acceleration of the vehicle for controlling the speed of the pilot motor thereby controlling the rate of acceleration oi' the motor.

12. In a motor control'system, in combination, a motor for propelling a vehicle, a source oi power !or the motor, switching means for connecting the motor to the source oi power, a plurality of resistors for controlling the motor current, a circular bus-bar, a plurality of contact members disposed to engage the bus-bar to shunt the resistors, a roller for actuating the contact members into engagement with the bus-bar, a

pilot motor for actuating the roller, a limit relay responsive to the motor current, and means responsive to the acceleration of the vehicle and cooperating with the limit relay to control the speed of the pilot motor, thereby controlling the rate of acceleration of the motor.

13. In a motor control system, in combination, a motor, a source of power for the motor, a plurality of resistors for controlling the motor current, a plurality of switches for shunting said resistors, additional resistor sections for controlling the motor current, a circular bus-bar, a plurality of contact members disposed to engage the bus- 'bar to shunt said resistor sections, a roller for pressing the contact members into engagement with the bus-bar, means for actuating the roller, and means associated with said switches for controlling the operation of the roller actuating means. i

14. In a motor control system, in combination, a plurality of motors, a source of power for the motors, a plurality of resistors for controlling the motor current, a plurality of switches for shunting said resistors in sequential relation, a plurality of additional resistor sections for controlling the motor current, a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar'to shunt said resistor sections, a plurality of rollers for moving the contact members into engagement with the bus-bar, means for actuating the rollers in unison, and means associated with said switches for controlling the operation of the roller actuating means.

15. In a motor control system, in combination, a plurality of motors, a source of power for the motors, a plurality of resistors for controlling the motor current, a plurality of switches for' for controlling the motor current, a circular busbar divided into a plurality of sections, a plurality of contact members disposed to engage the busbar to shunt said resistor sections, a plurality oi rollers for pressing the contact members into engagement with the bus-bar, a pilot motor for actuating the rollers in unison, means associated with said switches for controlling the energization 01 said pilot motor, and means responsive to the main motor current for controlling the speed of the pilot motor.

16. In a motor control system, in combination, a plurality of motors having series field windings, a source 01' power for the motors, a plurality of resistor sections for controlling the motor current, a circular bus-bar divided into a plurality of sections, a plurality of contact members disposed to engage the bus-bar to shunt the resistor sections, a plurality of rollers for pressing the contact members into engagement with the busbar, means for actuating the rollers, switching means for shunting said series field windings, means for energizing said switching means, and means responsive to the motor current for controlling the operation of said switching means.

17. In amotor control system, in combination, a plurality of motors having series field windings. switching means for establishing dynamic braking connections for the motors, means for successively shunting the field winding: )i' the motors by interlock progression during y amic braking, and means responsive to the motor current for controlling the operation of the field shunting means.

18. In a motor control system, in combination, a plurality of motors having series field windings, switching means for establishing dynamic braking connections for the motors, a master controller for controlling the operation of said switching means, resistors for controlling the motor current during dynamic braking, switching means for shunting the resistors, means for successively shunting the field windings of the motors by interlock progression during dynamic braking, and means responsive tothe motor current for controlling the operation of the field shunting means.

19. In a motor control system, in combination, a plurality of motors having series field windings, switching means for establishing dynamic brakmenses ing connections for the motors, means for successively shunting the field windings of the motors by interlock progression during dynamic braking, and relay means responsive to the motor current for controlling the operation of the first of said successive shunting means.

20. In a motor control system, in combination, a pair of motors having series fleld windings, means for cross connecting said motors during dynamic braking, means for successively shunting the field windings of the motors by interlock progression during dynamic braking, and relay means responsive to the current in both motors for controlling the operation of the first of said successive shunting means.

LYNN G. RILEY. 

